A second group of evolutionary markers, namely, the glyceraldehyde- 3-phosphate dehydrogenases (GAPDH) from Streptococcus faecalis, Pediococcus cerevisiae, Lactobacillus acidophilus and Streptococcus mutans, are currently being purified to homogeneity. These enzymes will be used as antigens to prepare GAPDH-specific antisera in rabbits which will subsequently be used to demonstrate structural relatedness among the GAPDHs of homo- and heterofermentative lactic acid bacteria. Results from biochemical and immunological experiments will be used to verify, where possible, and extend the phylogenetic map that was constructed from results of a similar study with the enzyme fructose diphosphate aldolase. The latter study demonstrated that species belonging to the genera, Streptococcus, Pediococcus, Lactobacillus, Acholeplasma, Propionibacterium Eubacterium, Butyribacterium and Aerococcus were derived from a common ancestor; the greater degree of ubiquity of the GAPDH should extend this list to include other genera.